We determined the clinical characteristics of chronic sinusitis in the patients with different lower respiratory tract diseases. Sinusitis was divided into three groups. The first group was sinusitis with bronchial asthma. The second group was sinusitis with chronic bronchitis, bronchiectasis or diffuse panbronchiolitis. This type of sinusitis is generally called sinobronchial syndrome (SBS). The third group was sinusitis without lower respiratory tract disease. Because the pathogenesis of these lower respiratory tract diseases differs with the diseases, the pathogenesis of sinusitis accompanied by these lower respiratory tract diseases also may be different. Clinical and laboratory examinations used in this study were rhinoscopy, X-ray examination of the paranasal sinuses, cytological study of nasal secretion and the saccharin test for the muco-ciliary function of the nasal mucosa. By rhinoscopic examination, no difference was found in the size of the nasal polyp among three groups. The results of other examinations were as follows. X-ray examination: Involvement of the ethmoid sinuses was greater than that of the maxillary sinuses in the patients with sinusitis with bronchial asthma. In contrast, involvement of the maxillary sinuses in SBS patients was greater than that of the ethmoid sinuses. Cytology of nasal secretion: Dominant inflammatory cells in the patients with sinusitis with bronchial asthma were eosinophils, while neutrophil were more frequently found in the SBS patients. Saccharin test: Most of the patients with bronchial asthma showed normal responses. In the SBS patients, however, only a few patients showed a normal response and the others showed prolonged responses. Clinical characteristics of the patients with sinusitis without lower respiratory diseases were more similar to those of the SBS patients. In conclusion, there were distinct differences in these clinical characteristics between sinusitis with bronchial asthma and SBS. These results suggest that the pathogenesis or the inflammatory process of sinusitis is heterogeneous and whether the inflammation is allergic or not may be important.